Electrochemical and Fluorescent Ferrocene-Imidazole-Based Dyads as Ion-Pair Receptors for Divalent Metal Cations and Oxoanions

In the tricyclic bis(heteroaryl)substituted ferrocenyl-imidazo-quinoxalines 7 and 8, the presence of redox and fluorescent units at the heteroaromatic core, which can act as a ditopic binding site, made these molecules potential candidates as electro-optical ion-pair recognition receptors. In this context, both molecules behave as ion-pair receptors for cations and anions, which individually had demonstrated their ability to form the corresponding cationic and anionic complexes. These receptors also show an important enhancement of anion binding by co-bound cations, whereas no affinity of the free receptors by the anion is observed. Similarly, receptors 7 and 8 display a dramatic increase in the cation binding by the action of their anionic complexes, while no affinity of the free receptors by the cations was detected. Interestingly, both receptors exhibit a remarkable enhancement of anions and cations binding, although no affinity of the free receptors by the ions is observed. In all cases, the ion-pair formation is detected by a perturbation of the redox potential of the ferrocene moiety and a remarkable enhancement in the emission band.